Note that perspective drawing techniques were not developed until the 14th and 15th centuries in Europe. The earliest techniques, developed by artists such as Albrecht Durer, used projection frames to assist in the accurate recreation of what they saw with their eyes. Exercise 10.1 gives an example of how you can use clear plastic as a plane of projection and capture a perspective view.

Refer to Figures 10.4 and 10.5 to see the locations of these features. In the profile view in Fig 10.4, note the angle made between the two projection lines going to the top and bottom of the near telephone pole (points A and B). Now look at the two projection lines going to points C and D on the far telephone pole and see how the angle between the two lines is much smaller. This angle, the visual angle, determines how large a real object is perceived by a human viewer and how large it would be represented in a perspective drawing.

Figure 10.8 demonstrates how the relationship between the horizon line (HL) and ground line (GL) determines the type of perspective view (i.e. human's eye, bird's eye, etc.).

Distance of the object from the picture plane

Position for the station point

Position of the ground line relative to the horizon line

Number of vanishing points

For example, the depiction of a toaster would probably have the object fairly close to the picture plane with the observer looking either straight ahead or slightly down at it (i.e. human's eye or bird's eye view). On the other hand, a large building would be farther away using either a worm's eye or ground's eye view, depending on how far the building is from the observer.

Inclined surfaces add considerable complexity to the layout of a perspective drawing. As with other types of pictorial drawing, inclined surfaces are drawn by first establishing points of reference along the primary dimensions and then constructing the inclined edges which make up the surface. Note that the inclined surface has its own vanishing point (point M in Figure 10.19).

As with other pictorial drawing methods, circles and curves are often plotted using a coordinate method and irregular curves. With sketching, the irregular curve can be dispensed with and the points connected freehand.

Just as with a hand-drawn perspective, defining the relationship between the viewer and the object is critical to a the creation of a successful pictorial. With most 3-D CAD systems, a viewpoint can be established anywhere with any cone of vision. The key is to set these variables so that the necessary geometric information is most clearly communicated to the viewer.